Method for the manufacture of hollow plastic articles

ABSTRACT

A method for manufacturing table tennis balls. The halves of a ball are formed in a single sheet and the sheet is separated to separate the formed halves of the ball. One of the portions of the sheet containing a ball half is inverted relative to the other and the portions are aligned so as to align the ball halves the rein. The sheet portions are then welded together to join the ball halves and the completed ball is removed from the joined sheet portions.

United States Patent Hurst et al.

[56] References Cited UNITED STATES PATENTS METHOD FOR THE MANUFACTURE OF HOLLOW PLASTIC ARTICLES WXXX M MM M 0 II I "/46 x5 1 m m "nu mnu m m "m um v H mm m b e m a 0W TRSJ 7048 3526 9999 11]] NN 11 [22] Filed: May 12, 1970 Primary Examiner-Robert F. White Assistant Examiner-J. H. Silbaugh Attorney-Rauber & Lazar [21] Appl. No.: 36,507

Related (1.8. Application Data [63] Continuation-impart of Ser. Nos. 601,591, Dec.

ABSTRACT l4, I966, abandoned, and Ser. No. 601,592, A method for manufacturing table tennis balls. The Dec. 14, 1966, abandoned.

halves of a ball are formed in a single sheet and the sheet is separated to separate the formed halves of the 7 Claims, 19 Drawing Figures mmmtmm 3105.932

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PATENTEDnEc 12 I972 SHEET lUUF18 SHEET IBUF 18 PKTE'N'TEDHH: 12 m2 METHOD FOR THE MANUFACTURE OF HOLLOW PLASTIC ARTICLES This invention relates to methods for the manufacture of hollow plastic articles particularly table tennis balls and is a continuation in part of our US. patent applications Nos. 601,591 and 601,592, both now abandoned.

Table tennis balls of the best quality are a precision product which must meet strict standards of weight and diameter and must be as nearly perfectly spherical as possible.

In the past table tennis balls have generally been made from cellulose nitrate by a method which involved forming ball halves from sheets of that material and attaching the ball halves together by treating the edges of the halves with solution one half being provided with a lip which fits inside the other half.

The fitting together of the halves is carried out largely by hand and the method suffers from the disadvantages that the cellulose nitrate and solvent used are highly inflammable and the accuracy of the method is poor so that a high proportion of low standard balls is produced, the balls having to be carefully graded.

Other types of ball which do not need to be made to a precise standard, e.g., hollow rubber balls, have been made by pressing ball halves in sheets of rubber and folding the sheets of rubber to bring the halves together.

This method cannot be applied, however, to the manufacture of table tennis balls since the stiff plastics materials needed to be used cannot be folded satisfactorily to give the required precision.

It has been proposed to make other low precision products, e.g., Christmas tree balls, by forming halves of the article in separate sheets of material and placing together the separate sheets to unite the halves of the article. This method produces inferior table tennis balls, however, since small differences in the thickness of the separate plastic sheets used cause the balls to be unbalanced.

According to the invention a method of manufacturing table'tennis balls comprises forming the two halves of a table tennis ball in a sheet of thermoplastic material, dividing the sheet into two separate parts each of which contains one half of said table tennis ball, invening one part of the sheet relative to the other part of the sheet by means of movable sheet gripping means and locating said two parts adjacent one another in superposed relationship so that the two halves of said table tennis ball are aligned in substantially the relative positions they occupy in the finished table tennis ball, joining said two parts together to form the table tennis ball and removing the table tennis ball from the sheet.

According to the invention also apparatus for use in the manufacture of hollow plastics articles comprises parting means for dividing the sheet into two separate parts each containing one half of the article, supporting means for the parts of the sheet, means for gripping one part of the sheet, means for producing relative movement between said one part of the sheet and its supporting means to move said one part of the sheet out of contact with its supporting means, means for inverting said one part of the sheet while it is out of contact with its supporting means, and means for locating the two parts together on the supporting means so that the halves of the article are in substantially the relative positions they occupy in the finished article.

Preferably the supporting means for the parts of the sheet is formed in two sections, one for each of the parts of the sheet, and the two sections are relatively movable to enable one part of the sheet to be moved out of contact with its supporting means to permit that part of the sheet to be inverted.

The method of this invention enables table tennis balls to be made to very high standards of precision economically and with a lower proportion of sub-standard balls than has previously been achieved.

The invention will now be described, by the way of example only with reference to the accompanying drawings in which:

FIGS. 1A, 1B, 1C together are a plan view of an apparatus for carrying out the method of invention.

FIG. 2 is a partial view of the apparatus in the direction of Arrow A of FIG. 1.

FIG. 3 is a partial view of the apparatus in the direction of Arrow B of FIG. 1.

FIGS. 4A, 48 together are a partial view in cross-section of the apparatus taken along the line C-C of FIG. 1

FIG. 5 is partial front elevation, partly in section, of the apparatus taken along the line D-D of FIG. 1.

FIG. 6 is a view partly shown looking in the direction of Arrow E of FIG. 5.

FIG. 7 is a cross-sectional view of the apparatus shown in FIG. 1 and looking in the direction of Arrow F of FIG. 1.

FIG. 8 is a partial view, partly broken away and sectional, taken in the direction of Arrow G of FIG. 7.

FIGS. 9A, 93 together are a partial view in cross-section, taken along the line H-H of FIG. 1.

FIG. 10 is a partial front view of the apparatus of FIG. 9 in the direction of Arrow K of FIG. 9.

FIGS. 11A, 11B and 11C together are views, partly in cross-section, of the apparatus, viewed along the line L-L of FIG. I and FIGS. 12A, 12B together are a view on Arrow M of FIG. 1 1B.

A table-tennis ball making machine is mounted on a rigid floor mounted frame 1 which has an invented T- shape cross-section. Located on the front face 2 of the vertical leg 3 of the frame are eight stations at equidistant centers. In each station is apparatus for performing one or more operations required during the manufacture of a table-tennis ball from a sheet of thermoplastic material. The stations are definitively titled feed station 100, heating station 200, forming station 300, cutting and doubling station 400, welding station 500, idle station 600, cropping and trimming station 700, and discharge station 800. Transferring means are provided for moving a sheet of material from one station to the next. Rotatably mounted on the base 4 of the frame at the rear of the central leg 3 is a camshaft 5 which extends the length of the frame. A plurality of cams is mounted on the camshaft and these are connected by cam followers to the apparatus and the transferring means to control the sequence of operations of the machine during manufacture. The camshaft is connected to a reduction gearbox 6 which is driven by a constant speed electric motor 7 so that the camshaft 5 rotates at a constant angular velocity.

The transferring means and the apparatus located in each station will now be described in more detail.

Transferring Means 

1. A method of manufacturing a table tennis ball comprising forming the two halves of a table tennis ball in a single, generally planar sheet of stiff thermoplastic material, dividing the sheet into two separate parts each of which contains one half of said table tennis ball, inverting one part of the sheet relative to the other part of the sheet by means of movable sheet gripping means and locating said two parts adjacent one another in superposed relationship so that the two halves of said table tennis ball are aligned in substantially the relative positions they occupy in the finished table tennis ball, joining said two parts together to form the table tennis ball and removing the table tennis ball from the sheet.
 2. A method according to claim 1 in which the sheet is divided into two equal parts by means of a knife.
 3. A method according to claim 1 in which one part of the sheet is held by sheet gripping means and inverted relative to the other part of the sheet by rotating said gripping means.
 4. A method according to claim 3 in which the inverted one part of the sheet is located on a support member by engagement of at least one ball half with a corresponding sized hole in the support member.
 5. A method according to claim 3 in which the other part of the sheet is located in superposed relationship with said inverted one part of the sheet by moving said other part of the sheet in the plane of said sheet relative to said inverted one part of the sheet by means of a pusher member.
 6. A method according to claim 5 in which a locating means is provided up to which said other part of the sheet is pushed by the pusher member to locate said other part of the sheet in superposed relationship with said inverted one part of the sheet.
 7. A method according to claim 6 in which the locating means is a stop. 